Dry-process porcelain enamelling of cast iron and like articles



T. TAFEL,'JR 2,952,558 DRY-PROCESS PORCELAIN ENAMELLING OF CAST IRON AND LIKE ARTICLES 5 Sheets-Sheet 1- Sept. 13, 1960 Filed Feb. 18, 1957 IOc mv ENTOKI THEODOKQ TAFEL, Jr.

ATTowY Sept. 13, 1960 T. TAFEL, JR 2,952,558

' DRY-PROCESS PORCELAIN ENAMELLING OF CAST IRON AND LIKE ARTICLES Filed Feb. 18, 1957 3 Sheets-Sheet 2 INVENTOK/ THEODOR TAFEL, J: Y

ATTO M EY Sept. 13, 1960 v T. TAFEL, JR 2,952,558

nawmaocsss PORCELAIN ENAMELLING OF CAST IRON AND LIKE ARTICLES Filed Feb. 18, 1957 5 Sheets-Sheet 3 INVENTQK THEODOFQTAFEL, Jr:

United States Patent ()fifice 2,952,558 Patented Sept. 13, 1960 DRY-PROCESS PORCELAIN ENAMELLING OF CAST IRON AND LIKE ARTICLES Theodore Tafel, Jr., 33 Elderwood Drive, Toronto, Ontario, Canada Filed Feb. 18, 1957, Ser. No. 640,692 Claims priority, application Great Britain Feb. 29, 1956 2 Claims. (Cl. 117-23) This invention relates to dry-process porcelain enamelling of cast iron and like articles.

Conventional practice in dry-process enamelling of cast on articles such as sanitary fixtures is to heat the article in the furnace to a temperature high enough to melt or sinter the enamel on contact, and then to deposit an even layer of enamel on the article by vibrating a sieve containing the dry powder over the surface to be enamelled.

A high degree of skill is required on the part of the enameller to properly distribute the enamel powder over the surface of the casting without loss of enamel and to supply as much enamel as possible before the temperature of the casting falls too low to melt or sinter the enamel. Wages for skilled labour thus form a large part of enamelling cost.

Since the enamel itself is cold, the application of the enamel cools the casting relatively quickly. The amount of enamel that can be applied at a single heating of the casting is therefore even more limited than it would be if the casting cooled in isolation, and it is customary for the casting to be returned to the furnace one or more times to enable the enameller to cover it properly.

Because most of the enamels now used have higher melting temperatures than those once used, to give greater acidresistance, the number of heating and enamelling stages required has increased. This has raised enamelling costs substantially.

i According to the invention, the substantial coo-ling eflect of the dry enamel is overcome by heating the enamel in a suitable furnace to a temperature slightly below its fritting temperature before it is applied by generally conventional methods.

The heated enamel powder has only an insignificant cooling effect on the casting, and a satisfactory coating can be applied in one operation on such articles as sinks and lavatories. In all cases, a greater quantity of enamel can be applied eifectively in a given time, the number of times the casting needs to be heated is reduced, and labour cost is cut substantially.

The use of heated enamel produces additional advantages in that the high temperature reduces the air content ofthe enamel, and causes the enamel to melt more quickly on contact with the cast iron, thus reducing the size and number of air bubbles formed and providing more time for air bubbles formed on the surface of the casting by chemical reaction with impurities in the iron to escape through the fluid enamel. In general it has been found that markedly better results are obtained by heating the enamel with agitation before application, and the agitation of the enamel during heating seems to improve the quality of the enamelled product.

, The invention contemplates careful heating of the enamel with thorough agitation in suitable apparatus, and

also contemplates preferred forms of heating furnaces for this purpose. It also contemplates heat-insulating sieves for applying the enamel and the preheating of the sieves before use, although these are not normally necessary for the carrying out of the process.

I ing a conventional gear speed reducer drives a pulley The objects and advantages of the invention are attained by the embodiment of the invention disclosed in the following description and the accompanying drawings which are of a preferred form of heating furnace for heating the enamel, and a preferred form of sieve for applying the enamel.

In the drawings, in which each reference character denotes the same part in the various views,

Fig. l is a side elevation, partly cut away to show the construction, of a suitable form of heating furnace for heating the enamel;

Fig. 2 is a side elevation of the furnace shown in operation feeding the enamel;

Fig. 3 is a fragmentary sectional view taken on the line 3--3 in Fig. 1;

Fig. 4 is a side elevation, partly cut away, to show the construction, of a modified form of heating furnace;

Fig. 5 is an end elevation, part-1y cut away, of the furnace;

Fig. 6 is a perspective view of a preferred form of sieve shown in operation applying enamel to a hypothetical work piece of cast iron.

It is important that the furnace for heating the enamel powder enables close control of the temperature to be achieved, because in general the greatest efficiency will be obtained from the invention if the enamel is heated to the highest possible temperature short of its sintering temperature. However, it is not in all cases necessary to heat the enamel to the maximum degree in order to gain the maximum benefit from the invention, for if a lower degree of heating is suflicient to enable the enamelling to be carried out in one stage, this will be sufficient; the saving in enamelling costs must be balanced against the cost of heating the enamel.

A suitable furnace for heating the enamel may consist of a drum arranged to rotate or vibrate or oscillate so as to agitate the enamel powder and increase the area exposed to thermal transfer, and supplied with effective heating and insulating means. In the preferred construction shown in the drawings, a cylindrical drum 10, with longitudinal fins No on its inner surface to pick up the particles of enamel and keep them in tumbling and mixing motion during the rotation of the drum, is arranged to rotate about its longitudinal axis on a shaft 11 sup ported on a frame 12. The drum has a conical end wall 10b tapering to meet the inner end of a cylindrical discharge spout 13, and it is supported on the shaft 11 by means of spokes 14. The shaft 11 rotates in bearings drumis surrounded by walls 20 of suitable insulating.

material.

The drum may be driven through a chain, belt or other suitable power transmission means from an electric motor or other source of power. In the preferred form shown, a pulley 21 driven by an electric motor 22 hav- 23 on the shaft 11 by means of a belt 24.

An alternative, more elaborate form of furnace for heating the enamel is shown in Figs. 4 and 5; a cylindrical drum 30, with longitudinal corrugations 30a in its cylindrical wall to mix the enamel during the rotation of the drum, is arranged to rotate about its longitu- 'dinal axis in a frame'31. The drum is driven by friction driving means including circular end plates 32 and 33 at the front and rear ends of the drum. The end plates extend radially beyond the circumference of the drum and rest oil-"rollers 34 and 35. The'front rollers 34 are preferably grooved to locate the drum axially while rear rollers 35 are idler rollers, smooth-surfaced to allow the edge of the end plate to slide axially on them, thus accommodating longitudinal expansion and contraction of the drum.

The end plates 32 and 33 partially close theends of the drum 30. At the front end, a cylindrical discharge spout 36 is mounted in the frontend plate 32, and the rear endplate has a central circular hole 37 through which enamel powder is introducedinto the drum by means of an obliquely disposed feed hopper 38 mounted on frame 31. The lower end o-f'the hopper extends into the drum through the hole 37and a flange 39 on the hopper keeps the end of the furnace substantially closed.

An electric motor 40 is used to drive the grooved rollers 34 through a conventional speed reducer and chain and sprocket drive transmission 41 that is well known and need not be specifically described.

The drum i's'preferablyheated by gas burners or electri'cal resistance means, as for instance by resistance elements 43 under the drum. A conventional thermocouple *44 may be used to control the temperature, and an insulated housing 45 surrounding the drum is supported on the frame 31 so that it does not come in contact with the revolving drum.

border to enable the enamel to be withdrawn from the furnace conveniently, the frame 12 in the form of furnace illustrated in Fig. 1, and the frame 31 in' the form of furnace shown in Fig. 4, are arranged so that the furnace can be mechanically tilted forwardly as shown in Fig. 2. In the arrangement shown, the furnace is supported on a base 46, and is pivoted to the base by a pivot 47 at the front of the furnace. An air cylinder 48 is secured at its upper end to the underside of the furnace and at its lower end to the base 46 by pivots 49and '50 respectively, so that actuation of the air cylinder 48 causes the enamel powder to move toward the discharge spout 13 or 36 as the case may be. If the furnace drum has a conical configuration like that of the furnace shown in Fig. 1, the powder will pass out the discharge spout directly on tilting. Where a flat front end plate is used however, as in the furnace shown in Fig. 4, radially arranged fins 51 may be disposed on the inside face of the front end plate 32 to carry enamel to the spout 36 as the drum 30 rotates. Other tilting means, such as a rack and pinion for instance, may of course be used instead of an air cylinder.

A typical vitreous porcelain enamel to the application of which the invention may be applied has the following formula Percent Si 45.5 Na O 15.4 13 0 3.5 CaO 2.7 PbO 14.2 Sb O 9.1 TiO I 6.4 K 0 1.5 Other 1.7

The enamel sinters at 1125 and shows slight adhes'ion of grain particles at 1070 F. Fusion begins at about 1200 F. A temperature of just under 1000 F. is suitable for heating this enamel in the furnace.

Generally a temperature of up to 100 below, and even up to below the sintering temperature is practical. The enamel will normally have to be heated up to at least 700 to obtain any substantial advantage from the heating step. Appropriate adjustment of the temperature is made for different enamel forniulations as required.

In order to retain the heat in theenamel while the enamel is being applied tothe metal article, the invention contemplates an insulated covered sieve 60. The design of the sieve, including a side wall 62, a screen 64 and a handle 66 secured to the side wall, with-a pneumatic or electric vibrator 68 on the handle, is generally conventional. 'According to the invention, however, the side wall is insulated in any suitable way, as for instance, by the incorporation of a sheet of Fiberglas insulation. Also according to the invention, a lid 72, insulated if desired in the same manner asthe'sidewall, as by the application of a disc of insulating ma l'terial to the cover, is pivoted to the side wall by'the hinge 74 and supplements the insulating effect of the side wall by preventing loss of heat. However, no speciallyinsulated form'of sieve is normally required to obtaintfle benefits of the invention.

-.It is to be understood that the form of the invention herewith shown and described is to be taken as'a preferred example of the same, and that various changes in the shape, size and arrangement of the parts may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

What I claim as my invention is:

1. In a 'method for coating, without heating during the coating operation, a metal article with asubStantially even layer of porcelain enamel over an extensive area of the surface thereof wherein said articleis heated prior to the coating operation to a temperature above the melting point of said enamel and enamel powder is deposited on said surface to be melted and form's'aid layer, the step of preheating said enamel powder in a container in heat exchange relation with but separated from a source of heat whereby direct contact of said enamel with the source of heat is prevented prior to deposition on the surface of said articlethe enamel being heated to a temperature below the sintering temperature of said enamel powder but sufficiently high to prevent substantial cooling of said'article upon contact with said enamel powder.

2. The method of claim 1 wherein said enamel powder is preheated prior to deposition on the surface of said metal article to a temperature within the range of 700 F. to 50 F. below the sintering temperature of said enamel powder.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A METHOD FOR COATING, WITHOUT HEATING DURING THE COATING OPERATION, A METAL ARTICLE WITH A SUBSTANTIALLY EVEN LAYER OF PORCELAIN ENAMEL OVER AN EXTENSIVE AREA OF THE SURFACE THEREOF WHEREIN SAID ARTICLE IS HEATED PRIOR TO THE COATING OPERATION TO A TEMPERATURE ABOVE THE MELTING POINT OF SAID ENAMEL AND ENAMEL POWDER IS DEPOSITED ON SAID SURFACE TO BE MELTED AND FORM SAID LAYER, THE STEP OF PREHEATING SAID ENAMEL POWDER IN A CONTAINER IN HEAT EXCHANGE RELATION WITH BUT SEPARATED FROM A SOURCE OF HEAT WHEREBY DIRECT CONTACT OF SAID ENAMEL WITH THE SOURCE OF HEAT IS PREVENTED PRIOR TO DEPOSITION ON THE SURFACE OF SAID ARTICLE THE ENAMEL BEING HEATED TO A TEMPERATURE BELOW THE SINTERING TEMPERATURE OIF SAID ENAMEL POWDER BUT SUFFICIENTLY HIGH TO PREVENT SUBSTANTIAL COOLING OF SAID ARTICLE UPON CONTACT WITH SAID ENAMEL POWDER. 